Meteorology 🌦️

The dry adiabatic lapse rate (DALR) is 9.8°C per 1,000 metres (approximately 1°C/100 m) — the rate at which unsaturated rising air cools. The saturated (moist) adiabatic lapse rate is lower at 4–6°C/1,000 m because condensation releases latent heat. DALR is used in crop-weather modelling, frost forecasting in hills, and understanding temperature inversions that trap cool air in valleys and damage sensitive crops.

The southwest (SW) monsoon normally arrives at Kerala around June 1, covers the entire country by July 15, and starts withdrawing from northwest Rajasthan around September 1, with complete withdrawal by October 15. The northeast (NE) monsoon brings rainfall to Tamil Nadu, Andhra coast, and Sri Lanka during October–December. IMD uses these dates for crop advisory and kharif crop planning.

The Planning Commission of India defined 15 agro-climatic zones based on soil, climate, and physiography: Zone I (Western Himalayan), Zone II (Eastern Himalayan), Zone III (Lower Gangetic Plains), Zone IV (Middle Gangetic Plains), Zone V (Upper Gangetic Plains), Zone VI (Trans-Gangetic Plains), Zone VII (Eastern Plateau and Hills), Zone VIII (Central Plateau and Hills), Zone IX (Western Plateau and Hills), Zone X (Southern Plateau and Hills), Zone XI (East Coast Plains), Zone XII (West Coast Plains), Zone XIII (Gujarat Plains and Hills), Zone XIV (Western Dry Region), Zone XV (Islands). ICAR subdivides these into 127 sub-zones.

Koppen classification uses letters based on temperature and precipitation patterns. In India: Af/Am (tropical rainforest/monsoon — Kerala, NE India), Aw (tropical savanna — most of peninsular India), BSh/BWh (semi-arid/arid — Rajasthan, Deccan), Cfa/Cwa (humid subtropical — Gangetic Plains, NE India), ET (tundra — high Himalayas). The 'A' (tropical) group dominates India's agricultural landscape.

A crop-weather calendar is a month-by-month chart correlating meteorological parameters (rainfall, temperature, humidity, sunshine hours) with crop growth stages, pest/disease incidence, and recommended agronomic operations. It is used by extension workers and KVK scientists to issue advisories — for example, issuing a blast disease alert in rice when temperatures are 25–30°C with high leaf wetness, or recommending late sowing of wheat when October temperature remains above 22°C.

Meteorology is directly tested in IBPS AFO (Professional Knowledge), NABARD Grade A/B, ICAR JRF (Agronomy and Agricultural Physics), and state PSC Agriculture Officer exams. The most frequently asked topics are: monsoon onset/withdrawal dates, agro-climatic zone count (15), lapse rate values, drought types, and climate classification systems.